There are many cases in which it is desired to measure organs or spaces within a patient's body. One such case is in preparation for organ transplantation. In transplantation procedures, in order to speed up the transplantation procedure and minimize the period in which the patient is without the transplanted organ, the new organ is preferably prepared before the transplantation procedure. In order to ensure proper reception of the new organ, it must be as similar as possible to the organ that is removed. In some organs the similarity in size may be approximate, since the surroundings of the organ are elastic. However, in other cases, the new organ must fit precisely in place of the old one.
In other cases, an empty space within a body is to be filled. For example, a patient may be missing a piece of a bone which is to be replaced by an artificial implant. Precise measurement of the space allows preparation of the artificial piece before its implantation, and may enable automatic fabrication of the artificial piece.
Measurements within a patient's body may be used also for other reasons, such as inspection and diagnosis. For example, in some cases, a tumor may be analyzed according to its size and/or its shape to track the progress of therapy or to plan a surgical operation. In tumor removal surgery, measurement of the tumor before, during, and after the surgery may be performed to verify removal of all or a desired portion of the tumor.
In the art, measuring an organ or a space within a body is usually performed on CT or MRI images, or using ultrasound. U.S. Pat. No. 5,370,692 to Fink et al., which is incorporated herein by reference, describes a method of approximately fabricating prosthetic bone implants according to a CT image. However, these measurements are less accurate than direct measurements of the bone dimensions. In addition, some organs have a complicated geometry and therefore are hard to measure even on accurate images. Furthermore, some organs, such as the heart, are in movement and cannot be imaged fast enough to allow production of a clear and still image which can be measured.
There has been a system proposed for producing a prosthetic device, based on an arm which is connected through motion detectors to a model carver. A tip of the arm is moved on an outer surface of an organ, so as to produce a model of the organ. The use of such arms is limited to organs which are easily accessible to the arm, and therefore in most cases this system cannot be used in minimally invasive procedures. In addition, using more than one arm simultaneously is very difficult, since multiple arms interfere with each other.
When aligning bones, regions between bone fractures should be of minimal size, to ensure that the bone properly heals. Ordinarily, one or more X-ray images are taken of the broken bone, and the pieces are aligned accordingly. However, when the fracture is complicated, many images may be necessary, causing the surgeon and patient to be exposed to large amounts of radiation.
U.S. Pat. No. 5,558,091 describes a method of aligning sections of a broken bone, by observing a continually-updated image. The image is initially acquired using X-rays, but is then updated by computer image processing, based on a position determining system which tracks the movements of sensors attached to the bones. However, this method requires producing a separate sub-image for each bone section, and therefore is not suitable for multiple fracture pieces. Also, it would be useful to have a method of accurately realizing the proper alignment of the bones independent of the images.